Rename some more relative paths to use @app path alias

frontend/src/app/previews.routing.module.ts

@@ -31,7 +31,7 @@ const routes: Routes = [
       },
       {
         path: 'lightning',
-        loadChildren: () => import('./lightning/lightning-previews.module').then(m => m.LightningPreviewsModule),
+        loadChildren: () => import('@app/lightning/lightning-previews.module').then(m => m.LightningPreviewsModule),
         data: { preload: true },
       },
     ],